Add example form documentation

Author: ahosgood

docs/example-form.md

@@ -0,0 +1,18 @@
+# The example form
+
+The configuration for the example form can be found in `app/forms/config/example-form.yml`.
+
+The flow is:
+
+```mermaid
+flowchart TD
+    pizza_or_chocolate -->|submit| food{food?}
+    food -->|pizza| pizza_topping
+    food -->|chocolate| type_of_chocolate
+    food -->|neither| neither_page
+    food -->|no_food_just_cats| reddit.com/r/catpictures
+    pizza_topping -->|submit| pizza_brand
+    pizza_brand -->|submit| address
+    address -->|submit| final_page
+    type_of_chocolate -->|submit| address
+```